1. Field of the Invention
The present invention relates to a mechanism for turning over a heavyweight object, e.g., a test-head, for 180.degree. so that it is turned upside down, in processes for manufacturing semiconductor devices, such as ICs, LSIs, etc., and more particularly, to a mechanism for rotatively transferring a high-frequency test head of wafer probing machine used in wafer tests for individually checking device patterns of semiconductor wafers.
2. Description of the Related Art
Semiconductor devices, such as ICs and LSIs, are subjected to several evaluation tests for their characteristics during their manufacturing processes. A wafer test process, which is a process for an electrical examination for each device pattern, is executed between a wafer test forming process and an assembly process, that is, after pretreatment processes, such as pattern etching and protective film coating.
A wafer test is intended to reject defective devices while they are each in the form of a wafer, and to feed test results back to the preceding process, thereby improving the yield and reliability of products.
A wafer test system basically comprises two apparatuses, a wafer probing machine (referred to also as a wafer prober) and a tester. These two apparatuses are connected to each other by means of a measuring line, and a test complete signal, fail signal, etc. are transferred between them in response to a test start command from a test control line.
In order to speed up tests, newly developed wafer test systems use a test head capable of high-frequency measurement, thereby shortening the measuring line and reducing the measuring time required.
The test head, which is in the form of a box, is supported on a wafer prober by means of a rotating mechanism. During a test, a performance board of the head is opposed to the top face of the prober. When the test head is off the test, it is rotated for 180.degree. so as to be turned upside down. The head contains a number of components, such as a high-frequency oscillator, and wires. If the number of pads on a device pattern increases, then the contained components and wires usually increase in number in proportion. Thus, the test head must be a large-sized, weighty object. A test head for probing high-integration devices, in particular, weighs extremely heavy. If its pins are 45 in number, for example, the head of this type weighs 25 kg or thereabout. If 256 pins are used, however, the head may be as heavy as about 100 kg.
Accordingly, the efficiencies of needle alignment (for contact between probe needles and their corresponding pads) and probe card replacement become too low to readily cop with the diversity of the test program. Thus, the test speed is lowered, as a whole. Since the test head is considerably heavy, moreover, it is very difficult to manually control its transfer.
In order to eliminate these awkward situations, mechanization of drive means for the test head rotating mechanism has been studied variously. Reversing mechanisms of a balance-weight type and a spring type have hitherto started to be practically used.
As shown in FIG. 1, a reversing mechanism of the balance-weight type is constructed so that weight 2 and test head 3 ar balanced with each other at point F. According to the balance-weight system, however, the total weight of the machine is increased, and the mechanism requires a wide installation space. Thus, the machine becomes heavier and bulkier. Since the weight of the test head varies depending on the type of subject devices, moreover, the balance between weight 2 and test-head is variety.
According to a reversing mechanism of the spring type, on the other hand, the machine can be reduced in weight. Like the mechanism of the aforesaid balance-weight type, however, the spring-type mechanism cannot smoothly revolve the test head throughout the stroke, and cannot, therefore, enjoy high operating efficiency. Furthermore, the force for supporting the test-head by the mechanism is poor, because the machine becomes heavier.